Conversion of polycyclic hydrocarbons



Unite 2,766,306 CONVERSION or rorvcrcrrc rrrnnocAnnoNs No Drawing. Application September 4, 1951, Serial No. 245,086

9 Claims. (Cl. 260668) The present invention relates to catalytic hydrocarbon conversion processes and is particularly concerned with conversion of polycyclic aromatic hydrocarbons to more valuable monocyclic products comprising benzene and monoand polyalkyl benzene compounds. These monocyclic products are desirable components of high octane gasoline and are also useful as individual compounds or fractions employed in the chemical industries as solvents or vehicles and as starting intermediates for synthesis of a large variety of important aromatic chemical compounds.

Polynuclear or condensed polycyclic aromatic hydrocarbon compounds including naphthalene and its homologues as well as hydrocarbons of more complicated multi-ring structure are generally found in fairly high concentration in the heavy residual fuels from thermal and catalytic cracking. These bottoms are unsuitable for recycling to the usual cracking process because of the refractory nature of these aromatic compounds; moreover the heavier portion when cracked under more severe conditions produces excessive amounts of coke. The same considerations apply to heavy hydrocarbon fractions from other sources rich in polycyclic hydrocarbons, including the residual stocks from lube oil refining such as Duosol and furfural rafinates, bottoms from distillation of crude oils of high aromaticity, as well as the residuum from hydrogenative reforming or hydroforming of naphtha fractions from petroleum.

It has now been found that it is possible to convert these refractory polycyclic aromatic hydrocarbons into more valuable monocyclic compounds of lower boiling point by a process involving hydrogenation of at least one ring of the polycyclic compound and cracking the thus formed partially hydrogenated compound. This is accomplished in accordance with the invention, by contacting the polycyclic aromatic hydrocarbons or a charge containing the same with a dual-function catalyst composed of a siliceous cracking component, such as silicaalumina, intimately combined with a minor amount of an active hydrogenating component, such as nickel, under proper operating conditions. These operating conditions comprise temperatures in the range of 800 to 1000 F. and hydrogen partial pressure of at least 1000 pounds per square inch, hydrogen being charged to the reaction zone in an amount equal to at least 3 mols per mol of hydrocarbon charged. Space velocities are selected so as to avoid overcracking of the charge While obtaining desired conversion, and generally lie in the range of 0.5 to 4 volumes oil per hour per volume of catalyst.

Under the conditions above set out maintaining an adequate hydrogen pressure throughout the reaction, deposition of coke on the catalyst can be kept to a minimum so that the process may be operated for long periods Without regeneration, or if desired regeneration at relatively infrequent intervals may be practiced.

In order to obtain the desired product distribution With best yields of monocyclic aromatic compounds from the hydrogenation and cracking of condensed polycyclic hydrocarbons, the dual-function catalyst utilized should be one having properly balanced activity as to the potential cracking function of the siliceous base and a quantity of nickel present therein.

While other catalysts comprising a hydrogenating component associated with a cracking component, such as molybdena on silica-alumina, are capable under properly selected conditions of hydrocracking polycyclic aromatics, these have not been found to exhibit the special selectivity characteristic of the catalyst of the invention comprising nickel in properly balanced proportion.

Since catalytic cracking activity is related to the acidity of the cracking catalyst-as explained for instance in Chemical characterization of catalyst by G. A. Mills, E. R. Boedeker and A. G. Oblad in Journal of the American Chemical Society (1950), volume 72, page l554-the relative crackingactivity of the cracking component of the catalyst is readily determinable by its capacity for chemisorption of an organic base. The use of such method for determining catalyst activity and the correlation of the values thus obtained with cracking activity determinations made by other methods, is reported in the periodical article referred to and involves a determination of the capacity of the cracking catalyst for chemisorption of quinoline; the relative activity or Quinoline No. being the milliequivalents of quinoline chemisorbed per gram of catalyst. This test has been found to correlate satisfactorily with catalytic cracking activity as determined by the Cat-A method (J. Alexander and H. G. Shimp, National Petroleum News (1944), volume 36, at p. R437; J. Alexander, Proc. Am. Petroleum Inst. (1947), volume 27 at p. 51) and other known methods.

The following procedure may be employed in determining the quinoline number of cracking component or" the catalyst, involving a highly accurate direct Weighing technique:

The catalyst is suspended in a perforated glass basket by a glass wire attached to one end of the beam of an analytical balance. Nitrogen at a constant pressure is then passed through a series of saturators containing liquid quinoline maintained at a constant temperature by a jacket containing boiling liquid. The nitrogen gas saturated with quinoline is passed through preheated vapor transfer lines into contact with the catalyst sample. Flow is continued until a relatively constant Weight is observed, and a stream of preheated nitrogen gas is then passed over the catalyst to remove physically held quinoline until a substantially constant Weight is observed. The difference in weight before contact with quinoline and after the nitrogen purge is taken as the amount of quinoline chemisorbed.

As an operative practical rule, dual-function catalysts displaying the required balance between the cracking and hydrogenating activities and thus furnishing the desired selectivity producing high yields of monocyclic aromatic hydrocarbons in the hydrogenative cracking of conjugated polycyclic compounds in accordance with the invention, are those wherein the quantity of the hydrogenating component such as metallic nickel, is present for each gram of catalyst in an amount approximately of 2.5 to 15 millimols per milliequivalent quinoline number of the catalyst. For instance, per 1000 grams of catalyst having a quinoline number of 0.06 milliequivaIent/gram, there should be present from about to about 900 mill-imols of nickel, corresponding roughly to form about 1 to 5% nickel by Weight of the catalyst.

Synthetic silica alumina catalyst of the bead or aggre gate pellet type having typical commercial activity of about 38 to 40 vol. percent gasoline (Cat-A) and corresponding to a quinoline number of 0.045 milliequivalent/gram should be incorporated with about 0.5 to 4% by weight nickel as hydrogenating component to provide a dual-function catalyst of desired balance activity. Cracking components of higher quinoline number going beyond the usual activities of commercial cracking catalysts accordingly require correspondingly larger quantities of nickel.

The catalyst employed in the process of the invent-ion should be one having a cracking activity of no less than about 30 vol. percent gasoline by the Cat-A method, corresponding to a quinoline number of about 0.025. Catalysts of this activity should contain, under the conditions stated, in the order of about 0.4 to 2.2 percent nickel by weight of the catalyst.

As compared with other types of catalysts which ordi- 'narily have shown acceptable activity in cracking at atmospheric pressure as well as with those adapted for hydrogena-tive cracking and destructive hydrogenation at higher pressures, the dual-function nickel catalysts above described, have been found to have an unusual selectivity in conversion of polycyclic hydrocarbons producing high yields of monocyclic compounds; cyclohexane ring type naphthenes that may also be formed in the process are readily dehydrogenated to desired benzene type aromatic compounds. The mechanism of the reaction is believed to involve primarily complete hydrogenation of one of the rings of the polycyclic compounds followed by splitting of the hydrogenated ring, which belief is substantiated by the fact that the product distribution experimentally obtained in conversion of tetralin is quite similar to that obtained in the conversion of :x-methyl naphthalene. Experimental work also appears to indicate that non-substituted rings are hydrogenated before substituted rings of a polycyclic hydrocarbon and that in the case of 3-conjugated ring systems the center ring is hydrogenated and split, giving rise to two mols of monocyclic aromatic compounds. The results thus experimentally obtained indicate that strong hydrogenative components and operating conditions favoring hydrogenation are beneficial.

In the following example there are shown the results obtained in conversion of rx-methyl naphthalene employing the described nickel catalyst on a synthetic silicaalumina base as compared with an operation under substantially identical conditions employing a dual-function catalyst composed of a small amount of molybdenum oxide on the same type silica-alumina base, which latter catalyst has proved to give some of the best results in hydrocracking of paratfinic gas oils.

EXAMPLE I The catalysts described in the following table were each contacted with a-methyl naphthalene at 900 F., under a total pressure of 2500 p. s. i, operating at a liquid space velocity of 2 volumes oil per hour per volume of catalyst, three mols of hydrogen per mol of the methyl naphthalene being added with the charge. The yields and products are reported in the following table:

The presence of tetralin in the products obtained with the nickel catalyst is indicative of the mechanism Of the reaction.

The nickel catalyst employed in the above example was composed of 2% by weight nickel on pelleted synthetic silica-alumina gel (87.5% SiOz, 12.5% A1203) of 45 activity (Cat-A), corresponding to about 5.5 millimols Ni per mill-iequivalent of the SiO2Al2O3 quinoline number.

With the same nickel on silica-alumina catalyst operating at 1000 pounds pressure only about 23% conversion of wmethyl naphthalene is obtained.

EXAMPLE II The same nickel on silica-alumina catalyst was also employed in the conversion of phenanthene (diluted with heptane) under the ope-rating conditions of Example 1, resulting in about 79% conversion with the production of over 64% alkyl benzenes.

EXAMPLE III The same type catalyst as in the previous examples was also employed in the hydrogenative cracking of refractory recycle stocks comprising (a) l-pass recycle from catalytic cracking, (b) 2-pass recycle, catalytic followed by thermal. There was obtained respectively 31% and 39% aromatics in the gasoline boiling range.

EXAMPLE IV The bottoms fraction from a hydroforming operation boiling in the range of 3l0-432 F. and substantially free of benzene, toluene, and xylenes, but containing naphthalene and its homologues, was subjected to hydrogenative cracking with silica-alumina-nickel catalyst similar to that employed in the previous examples and under conditions of Example I except for higher hydrogen supply (6 mols H2 per mol oil). The yields are reported below:

Table 2 Liq. products, wt. percent 87.0 Dry gas, wt. percent 7.7 C4s wt. percent 2.9 Css wt. percent 2.0 Coke wt. percent 0.4 Initial-toluene, wt. percent chg 4.7 Toluene, wt. percent chg 6.4 Xylene, wt. percent chg 26.3 C3 benzenes, wt. percent chg 36.0 ISO-205 C., wt. percent chg 10.1 Above 205 C., wt. percent chg 9.5

While the charge does contain C3 benzenes, the quantity of such in the products is in the order of about twice that in the charge, indicating that conversion of polycyclic to monocyclic aromatics has occurred as well as dealkylation.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim as our invention:

1. The method of forming aromatic monocyclic hydrocarbons from polycyclic aromatic hydrocarbons in a charge stock containing the latter, which comprises subjecting such a charge stock to hydrogenative cracking in contact with a catalyst comprising a siliceous cracking component intimately combined with a minor quantity of nickel, said cracking component having an acidity corresponding to a quinoline chemisorption capacity of not less than 0.025 milliequivalents per gram and the quantity of nickel in said catalyst being correlated with the acidity of the cracking component such that the catalyst contains 2.5 to 15 millimols Ni per milliequivalent quinoline chemisorption capacity of the cracking component, such con tact being effected at a temperature of 800-1000 F., un der a hydrogen partial pressure of at least 1000 pounds per square inch, hydrogen being added in an amount equal to at least three mols per mol of charge stock.

2. The method as defined in claim 1 wherein said charge stock is a refractory recycle stock from pyrolytic cracking.

3. The method as defined in claim 1 wherein said charge stock is a recycle stock from catalytic cracking and boils predominantly in the range above gasoline.

4. The method as defined in claim 1 wherein said gel has a chemisorption capacity of 0.06 milliequivalent quincline per gram and contains about 1 to 5% nickel by weight of the catalyst.

5. The method as defined in claim 1 wherein said catalyst comprises silica-alumina gel having a Cat-A activity index of 38-40 and contains 0.5 to 4% by weight nickel.

6. The method of forming aromatic monocyclic hydrocarbons from polycyclic aromatic hydrocarbons in a charge stock containing the latter, which comprises contacting such a charge stock at elevated temperature and at super-atmospheric partial pressure of hydrogen with a catalyst consisting of a minor quantity of nickel intimately associated with a silica-alumina base having a cracking activity corresponding to a Cat-A activity index of not less than 30, the quantity of nickel being correlated with the cracking activity of the base as determined by the quinoline chemisorption capacity of the base, and corresponding to 2.5 to 15 millimols nickel per milliequivalent chemisorption capacity of the base.

7. The method according to claim 6 wherein such contacting is carried out at a temperature in the range of 800-1000" F. and at a hydrogen partial pressure of at least 1000 pounds per square inch, at least 3 mols of hydrogen being added per mol of hydrocarbon charged.

8. The method according to claim 6 wherein said charge stock comprises recycle stock from a catalytic cracking operation.

9. The method of upgrading a residual hydrocarbon fuel from pyrolytic conversion operations which fuel is rich in polycyclic aromatic hydrocarbons, which method comprises contacting such a fuel at a temperature of about 800-1000 C. and under a partial hydrogen pressure of at least 1000 pounds per square inch, with a catalyst comprising silica-alumina base having nickel uniformly associated therein, said base having a cracking activity corresponding to a CatA index of 38-45 and said catalyst containing 0.5 to 5% by weight nickel.

References Cited in the file of this patent UNITED STATES PATENTS Kennedy et al Dec. 2, 1947 V-oorhies et a1 Mar. 15, 1949 OTHER REFERENCES 

1. THE METHOD OF FORMING AROMATIC MONOCYCLIC HYDROCARBONS FROM POLYCYCLIC AROMATIC HYDROCARBONS IN A CHARGE STOCK CONTAINING THE LATTER, WHICH COMPRISES SUBJECTING SUCH A CHARGE STOCK TO HYDROGENATIVE CRACKING IN CONTACT WITH A CATALYST COMPRISING A SILICEOUS CRACKING COMPONENT INTIMATELY COMBINED WITH A MINOR QUANTITY OF NICKEL, SAID CRACKING COMPONENT HAVING AN ACIDITY CORRESPONDING TO A QUINOLINE CHEMISORPTION CAPACITY OF NOT LESS THAN 0.025 MILLIEQUIVALENTS PER GRAM AND THE QUANTITY OF NICKEL IN SAID CATALYST BEING CORRELATED WITH THE ACIDITY OF THE CRACKING COMPONENT SUCH THAT THE CATALYST CONTAINS 2.5 TO 15 MILLIMOLS NIPER MILLIEQUIVALENT QUINOLINE CHEMISORPTION CAPACITY OF THE CRACKING COMPONENT, SUCH CONTAT BEING EFFECTED AT A TEMPERATURE OF 800-1000* F., UNDER A HYDROGEN PARTIAL PRESSURE OF AT LEAST 1000 POUNDS PER SQUARE INCH, HYDROGEN BEING ADDED IN AN AMOUNT EQUAL TO AT LEAST THREE MOLS PER MOL OF CHARGE STOCK. 